1. Field of the Invention
The present invention relates to an immersion exposure technique used in manufacturing a semiconductor device and, for example, to an immersion multiple-exposure method and immersion exposure system for separately performing multiple exposure of micropatterns and non-micropatterns.
2. Description of the Related Art
In a recently proposed technique, in forming a highly integrated semiconductor circuit device, patterns to be exposed are divided into micropatterns and non-micropatterns and double-exposed to a photoresist film under illumination conditions optimum for the respective patterns (e.g., Jpn. Pat. Appln. KOKAI Publication No. 2000-349010). Immersion exposure will be described as an example. First, an ArF organic anti-reflection material is applied to the element formation surface (major surface) of a wafer by spin coating and baked at 215° C. for 1 minute, thereby forming an 80-nm-thick anti-reflection film. Then, an ArF positive resist is applied to the anti-reflection film by spin coating and baked at 90° C. for 1 minute, thereby forming a 400-nm-thick photoresist film. Next, an immersion exposure protective film is applied to the photoresist film by spin coating and baked at 90° C. for 1 minute.
An ArF excimer laser immersion exposure apparatus exposes the wafer having the stacked structure of the anti-reflection film, photoresist film, and immersion protective film using a halftone mask having a transmittance of 6% under conditions of NA=0.78 and ⅔ annular illumination. The wafer is exposed again using a halftone mask having a transmittance of 6% under conditions of NA=0.92 and σ0.97. The wafer is baked at 100° C. for 1 minute and developed in a 2.38-wt % aqueous solution of tetramethylammonium hydroxide (TMAH), thereby forming a resist pattern.
When the resist pattern formed by the above-described double-exposure was inspected by an optical defect inspection apparatus (2360 available from KIA), a number of defects were found, and the defect density was about 0.7 pieces/cm2. These defects are presumably produced upon double-exposure in immersion exposure because dust particles produced in the first exposure step stick to the immersion protective film and shield the irradiation light in the second exposure step.